The present invention relates to an inspection unit for a high-frequency/high-speed device for ensuring reliable connection between the inspection unit and the device to be inspected, on occasion of inspecting its electrical performance, before a module of a high-frequency/high-speed circuit such as an amplifier circuit, a mixer circuit, a filter circuit, a memory, a CPU, etc. or an IC to be incorporated in a mobile phone, for example, is assembled to a circuit board. In this specification, the term “high-frequency” refers to an analogue signal having a high-frequency (1 GHz or more), while the term “high-speed” refers to a digital signal having very narrow pulse width and short pulse interval, and both of which are hereinafter collectively referred to as RF (radio frequency).
On occasion of inspecting electrical performance of the RF device such as a semiconductor wafer, an IC, or a module, insufficient contacts between the terminals may particularly cause fluctuation of impedance or other measurement factors, which may sometimes vary to change measured values. Under the circumstances, such inspection is conducted by a special inspection unit, for example, as shown in FIG. 8A (disclosed in Japanese Patent Publication No. 2001-99889A). In such an inspection, an RF circuit, which is the device to be inspected, is constructed in a form of a module 50 including an amplifier circuit and a mixer circuit, and is housed in a metal casing for avoiding interference with the exterior. The module 50 includes input and output terminals 51, 54 for RF signals, a power supply electrode terminal 52, and a grounding terminal 53, which are provided on a back face of the metal casing. Then, the inspection is conducted by electrically connecting the terminals to respective terminals of a wiring board 66 on which certain wirings for the inspection are arranged.
In this example, there are employed contact probes each having a spring and a plunger contained in a metal pipe, one end of the plunger being adapted to be projected to the exterior by the spring and contracted when pushed. The respective electrode terminals are connected by contact probes 63 for RF signals, a contact probe 64 for power supply, and a contact probe 65 for grounding which are contained in a metal block 61 for preventing them from being affected by noises. Each of the contact probes 63 for RF signals is formed in a coaxial structure, using the contact probe as a core conductor and using an inner wall of a through hole in the metal block 61 as an outer conductor, especially for preventing intrusion of noises. In this example, the contact probe is so constructed that a hollow space is formed between the inner conductor (the RF contact probe 63) and the outer conductor (the inner wall of the through hole in the metal block 61) of the coaxial structure so as to obtain a smaller diameter of the contact probe in order to cope with the narrow pitch. For this reason, insulating O-rings 69 are fitted to the contact probe 63 for RF signal, as shown in a partially enlarged view of FIG. 8B, so that the contact probe 63 for RF signal can be held in the hollow space.
Meanwhile, the contact probe 65 for grounding is inserted into the metal block 61 with a ground socket 65a being interposed, thereby to avoid deformation and to obtain favorable contact with the metal block 61. On the other hand, the contact probe 64 for power supply is inserted into the metal block 61 with an insulating tube 64a being interposed so as not to come into contact with the metal block 61. In FIG. 8A, denoted by numeral 67 is a coaxial cable, and 68 is a plate for retaining the metal pipes which form outer shells of the contact probes. Also in the case of an IC socket for inspecting the IC, the structure around the contact probe is almost the same, though it has a different outer shape.
As described above, it is possible to reduce a diameter of each through hole, in a case where a metal block is employed and a coaxial structure is formed by making a hollow space between the inner wall of the metal block as an outer conductor and a probe for RF signal as an inner conductor. This enables the whole unit can be made small, and it is possible to inspect even the device in which the electrode terminals are provided at a narrower pitch, while regulating the impedance. However, it is necessary to form through holes in the metal block 61 formed of metal such as brass or aluminum at a pitch of about 0.4 to 1 mm, requiring high manufacturing accuracy of about ±10 μm. Under the circumstances, there is a problem that it is difficult to substitute the metal block with a die-casting product, and even though it is substituted with the die-casting product, the through holes must be respectively produced by cutting works, which will lead to enormous increase of production cost.
Additionally, the probe for power supply must be isolated from the metal block. In a case where an interval between the contact probes is so set as to have a narrow pitch less than 0.5 mm, for example, a diameter of the probe for power supply must be inevitably smaller in order to cover the contact probe for power supply with an insulating tube. Therefore, there are such problems that cost for inserting the insulating tube will increase, and that contact resistance will increase in the probe for power supply.